Update src/tools/make_ctags to avoid Exuberant tags option that has been renamed and undocumented since 2003;  instead, use the documented option.  Add comments.
Update src/tools/make_ctags to avoid Exuberant tags option
that has been renamed and undocumented since 2003;  instead, use the
documented option.  Add comments.

adam8157/gpdb,adam8157/gpdb,zeroae/postgres-xl,jmcatamney/gpdb,xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,snaga/postgres-xl,yazun/postgres-xl,arcivanov/postgres-xl,yazun/postgres-xl,50wu/gpdb,50wu/gpdb,ovr/postgres-xl,kmjungersen/PostgresXL,snaga/postgres-xl,ashwinstar/gpdb,pavanvd/postgres-xl,xinzweb/gpdb,yazun/postgres-xl,jmcatamney/gpdb,Postgres-XL/Postgres-XL,arcivanov/postgres-xl,kmjungersen/PostgresXL,ovr/postgres-xl,50wu/gpdb,lisakowen/gpdb,lisakowen/gpdb,oberstet/postgres-xl,snaga/postgres-xl,tpostgres-projects/tPostgres,lisakowen/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,jmcatamney/gpdb,kmjungersen/PostgresXL,xinzweb/gpdb,postmind-net/postgres-xl,tpostgres-projects/tPostgres,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,tpostgres-projects/tPostgres,greenplum-db/gpdb,techdragon/Postgres-XL,lisakowen/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,adam8157/gpdb,techdragon/Postgres-XL,yazun/postgres-xl,jmcatamney/gpdb,Postgres-XL/Postgres-XL,zeroae/postgres-xl,pavanvd/postgres-xl,50wu/gpdb,postmind-net/postgres-xl,kmjungersen/PostgresXL,ashwinstar/gpdb,greenplum-db/gpdb,postmind-net/postgres-xl,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,techdragon/Postgres-XL,jmcatamney/gpdb,50wu/gpdb,50wu/gpdb,ashwinstar/gpdb,xinzweb/gpdb,adam8157/gpdb,snaga/postgres-xl,postmind-net/postgres-xl,tpostgres-projects/tPostgres,yazun/postgres-xl,pavanvd/postgres-xl,xinzweb/gpdb,zeroae/postgres-xl,ashwinstar/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,tpostgres-projects/tPostgres,oberstet/postgres-xl,adam8157/gpdb,greenplum-db/gpdb,adam8157/gpdb,kmjungersen/PostgresXL,arcivanov/postgres-xl,lisakowen/gpdb,zeroae/postgres-xl,arcivanov/postgres-xl,pavanvd/postgres-xl,zeroae/postgres-xl,50wu/gpdb,techdragon/Postgres-XL,arcivanov/postgres-xl,snaga/postgres-xl,lisakowen/gpdb,ovr/postgres-xl,oberstet/postgres-xl,Postgres-XL/Postgres-XL,greenplum-db/gpdb,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,postmind-net/postgres-xl,adam8157/gpdb,ovr/postgres-xl,Postgres-XL/Postgres-XL,Postgres-XL/Postgres-XL,ashwinstar/gpdb,ovr/postgres-xl,arcivanov/postgres-xl